In recent years, with the rapid development of high-speed electrophotographic laser printers and copy machines, there is an increasing demand for toners with better developability, transferability and low-temperature fixability. In the recent toner development, out of environmental considerations, low-temperature fixability is especially an essential factor since it can lead to decrease in power consumption.
Along with the expansion of the market, the environment of usage has increasingly diversified, and toners have been demanded to deliver stable performance in a wide range of environments, from a low temperature and low humidity environment to a high temperature and high humidity environment. Accordingly, the development of toners that can provide excellent durability in different environments and low-temperature fixability, has been studied.
For example, a polymerized toner is disclosed in Patent Literature 1, which is obtained by polymerizing a polymerizable composition that contains a polymerizable monomer, a colorant and a liquid polymer having a glass transition temperature of 0° C. or less. It is also disclosed that the toner is excellent in low-temperature fixability, environmental stability and printing durability and ensures good image reproducibility. In Patent Literature 2, it is disclosed that a toner manufactured from a toner composition in an aqueous medium, the toner composition containing a polymerizable monomer, a colorant, a polar resin and a fine powder material insoluble with styrene and the toner containing the polar resin in a specific amount and satisfying a specific relational expression between the acid value of the binder resin, the acid value of the polar resin and the acid value of an organic compound treating the surface of the fine powder material, is excellent in environmental stability and charging characteristics and is also capable of achieving a high-quality image, without causing image density irregularity, etc.
A yellow toner is disclosed in Patent Literature 3, which has toner particles obtained by polymerization of a polymerizable monomer composition containing a polymerizable monomer, a yellow pigment, a wax and two kinds of carboxyl group-containing resins, wherein the carboxyl group-containing resins are contained in specific amounts and the interfacial tension of styrene, the interfacial tension of the yellow pigment and the interfacial tensions of the carboxyl group-containing resins satisfy specific relational expressions. It is also disclosed that the yellow toner is excellent in low-temperature fixability, high in glossiness and tinting strength, and excellent in transparency. In Patent Literature 4, a toner containing toner particles obtained by granulation of a binder resin, an ester wax and a carboxyl group-containing vinyl resin in an aqueous medium is disclosed, wherein the SP value of the binder resin and the SP value of the carboxyl group-containing vinyl resin are in given ranges; the molecular weight and the molecular weight distribution of the carboxyl group-containing vinyl resin are in given ranges; and the content of the ester wax and the content of the carboxyl group-containing vinyl resin are in given ranges. It is also disclosed that the toner is able to prevent decrease in durability and contamination in fixing devices, as well as it is able to provide both low-temperature fixability and storage stability at high temperature.
However, the toners obtained by the methods disclosed in these patent literatures are difficult to satisfy, in response to the recent demand for high speed printing, both low fixing temperature and storage stability at high temperature concurrently and sufficiently. In addition, they are sometimes insufficient in printing durability under different environments.